The proposed study is aimed at investigating the transport and deposition of hygroscopic aerosols in glass models of the respiratory tract under humid conditions as well as in the lungs of anesthetized dogs. In the first phase of the study, glass models will be used to investigate the effects of particle size, chemical composition of the particles, and air flow rate on deposition. A mechanical breathing machine will be used to simulate the respiratory flow. The results will be compared with the deposition data of non-hygroscopic aerosols. In the second phase of the study, animal models will be developed and used to investigate the effects of particle size, breathing pattern, and chemical composition of the particles on deposition. The regional distribution of the deposited particles will be studied using aerosols generated from the glass model and the animal model will be used to develop a mathematical model for predicting the deposition of hygroscopic particles in the human respiratory tract. Such a mathematical model should have application in aerosol therapy.